Just ask filmmaker Errol Morris, who has taken on both controversial former Defense secretaries as documentary subjects in their twilight years: McNamara in 2003's "The Fog of War," and now Rumsfeld in "The Unknown Known," which had its world premiere at the Telluride Film Festival over Labor Day weekend.

"The Fog of War," which won a documentary Oscar, revealed McNamara, a chief architect of the Vietnam War, as a reflective man in his late 80s willing to acknowledge errors of judgment. That film was divided into 11 segments, each one nominally corresponding to a lesson McNamara had learned during his lifetime, including "empathize with your enemy" and "belief and seeing are both wrong."

In contrast, "The Unknown Known" — its title ironically derived from one of Rumsfeld's favorite axioms about knowledge and how to evaluate situations — is a forceful portrait of another octogenarian who prefers using language to explain and obfuscate, trying to cast his own history while seemingly denying doing any such thing.

The film is largely composed of a smiling Rumsfeld, 81, staring straight into the camera while reading a series of his memos and answering questions that Morris poses. The footage doesn't contain any bombshells — those hoping only to see Rumsfeld confess that he knew there were no weapons of mass destruction in Iraq or say that the invasion was ultimately hardly as successful as the George W. Bush administration insisted, will likely be disappointed.

"You believe that in writing these memos, he's writing down in part what he thinks and in part what he wants people to believe he thinks — and you never clearly know which is which," Morris said in an interview.

Even those who admire Rumsfeld may find his rhetorical devices frustrating — he plays his cards so close to the vest, for example, that he refuses to acknowledge that the Vietnam War was a failure for reasons other than chance. "Some things work out, some things don't," he says. "That didn't."

But the sum of Rumsfeld's responses does paint a picture of a man — one who seems to be hiding in a fortress surrounded by a moat of words. No matter how hard Morris tries to traverse the moat, the former Defense secretary throws out more verbiage. Rumsfeld says at one point, "All generalizations are false. Including this one."

"I think there's actually a lot that is being said," Morris said. "What struck me is that he often would be talking about himself without clearly knowing it. He would be talking about [Iraqi Deputy Prime Minister] Tariq Aziz, and he'd really be talking about himself. He would be talking about Saddam Hussein, and he'd really be talking about himself. He'd be talking about a soldier he visited at Walter Reed Hospital who he thought was dying, and he'd be talking about himself."

The 65-year-old Morris, whose films include "The Thin Blue Line" and who is the author of several books, including "A Wilderness of Error: The Trials of Jeffrey MacDonald," sent Rumsfeld a DVD of "Fog of War" to help pitch the idea of making a documentary. But the filmmaker said that when he first met Rumsfeld in person, he felt it was Rumsfeld himself who was doing the selling. (Although Morris showed Rumsfeld several versions of "The Unknown Known" before it was finished, Rumsfeld had no editorial control over the film.)

"It's his hope that words can save him," Morris said. "If only he can come up with the appropriate definitions, everything will be OK." In one memo, Rumsfeld writes about eliminating certain words — including quagmire — from the Pentagon dictionary.

While McNamara had more than 30 years to assess his actions before sitting down with Morris, Rumsfeld has had only about a decade of distance since the start of the Iraq war. Yet even when discussing incidents and memos that are decades old, Rumsfeld on camera follows a similar script, rarely conceding, let alone reflecting upon, any possible misstep.

At the film's conclusion, Morris asks Rumsfeld why he wanted to participate in the project.

"I'll be damned if I know," the former Defense secretary replies. Likewise, moviegoers may be more mystified by Rumsfeld after watching the documentary than they were before. But as Morris sees it, that's just fine.

"The mystery of the film," Morris said, "is that you wonder: Is there more that's being hidden? Or is that it?"

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